There is a known technology that uses solder to join electrodes together. Solder including tin (Sn) and Pb-free solder that does not include lead (Pb) are known as the solder that is used to join electrodes. Also, low melting point solder of a comparatively low melting point, such as solder including indium (In) and solder obtained by adding an element such as silver (Ag) to the solder including indium (In), is known.
See, for example, Japanese Laid-open Patent Publication Nos. 2013-233577 and 2011-005542, and International Publication Pamphlet No. WO 2009/051255.
When the solder including Sn is joined with an electrode including copper (Cu) so as to form alloy of Cu and Sn at a boundary between the solder and the electrode, voids and cracks tend to be formed at the boundary, decreasing joint reliability between the solder and the electrode.